The present invention concerns a push-button which is very well suited to use in an electronic watch or in any other electronic device of relatively small dimensions.
As is known, in the field of horology, the case of a watch is an essential element. In the case of electronic watches, the case contains, amongst other things, a battery or a rechargeable accumulator, as well as a quartz oscillator which provides, via a frequency divider circuit, a time base to a control circuit allowing a digital liquid crystal display to be controlled or a stepping motor, able to drive a conventional gear train and a set of hands, to operate. It is thus indispensable for the case to be water resistant and damp proof.
However, push-buttons have to pass through these cases. With a few rare exceptions (touch sensitive keys for example), these push-buttons are, in the current state of the art, indispensable to be able to control the horological functions of a watch necessary, for example, to start a chronograph or reset the time of the watch.
Push-buttons are buttons which project from the middle part of the watch. By pushing them with a finger, the desired watch function is activated. The push-button thus puts the positive pole of the battery or accumulator in contact with the negative pole of the electronic control module which contains, in particular, the time setting programme. Depending on the nature of the pulse, the hands or the time indication provided by the liquid crystal display is moved forward, either minute by minute (short pulse) or by an hour (long pulse). When the pressure ceases, the push-buttons return to their initial place.
The construction of these push-buttons is usually quite complex. They are generally formed of a push-button head which may be driven or bonded onto a push-button stem. The push-button stem is arranged so as to slide inside a housing arranged in the middle part of the watch which has to be made with great precision. The push-button stem moves axially in this housing against the return force of a spring when pressure is applied on the push-button head. The return spring is usually arranged in a housing arranged in the push-button head and rests axially on the bottom of a cavity provided in the middle part. According to a variant, a contact strip which has resilient properties, acts as the return spring and prevents the stem from escaping from the housing in which it slides. Finally, in order to ensure the sealing of these push-buttons, sealing gaskets are used. Unfortunately, over time, these sealing gaskets become dirty and hard, which causes sealing deficiencies which may be detrimental to the proper operation of the watch.
On the other hand, as mentioned hereinbefore, the push-buttons project from the middle part of the watch. They thus form protuberances which impair the aesthetic appearance of the watch.
Finally, these push-buttons, projecting from the middle part of the watch, may be handled inadvertently, for example by being caught on the wearer""s shirt or jacket sleeve, which may cause a function of the watch to be inadvertently activated or the settings of the watch to be disturbed.
In order to overcome these drawbacks, correctors are already known. These are also buttons, but they are embedded in the middle part of the watch. Like push-buttons, they are used to adjust the different indications given by an electronic watch for example. These correctors can only be activated using a pointed element which enables them to be pushed. Aesthetically, correctors allow a middle part free of any protuberances to be achieved. However, their structure is as complicated as that of a push-button and they are thus expensive to make.
There is also known from GB Patent No. 2 077 506 in the name of Citizen, a watch case having push-buttons wherein stem and external push-button head are made in a single moulded plastic piece. The head has a wall which is thin enough to be slightly flexible, thus allowing the stem a small travel, and acting as a return spring. The free end of the stem bears a conductive rubber plate which, when the push-button is pushed in, is applied onto two fixed contacts to connect them electrically. The periphery of the flexible head is in the shape of a cylindrical skirt which, in a first embodiment of the push-button, is bonded in a sealed manner against the wall of the case. In another embodiment, the moulded part is made in a single piece with the case, the skirt being directly connected to the case.
Such a push-button head has to have a large enough diameter for the head to be flexible. This is possible in the case of the aforecited document because the push-buttons are located on an upper face of the case. Conversely, they could not be located on the lateral wall of the case (the part called the middle part), because the height is generally very limited. Further, repeated bending of the flexible plastic head is liable over time to cause the skirt to become unstuck or to split it, thereby affecting the sealing and operation of the push-button. It is also to be noted that the push-button head projects from the top surface of the case. It thus impairs the aesthetic appearance of the watch and may be activated inadvertently.
The main object of the present invention is thus to overcome the aforementioned drawbacks of the prior art in addition to others by proposing a push-button which can be made economically by a method for injecting plastic material such, that the push-button cannot be activated inadvertently.
The present invention therefore concerns a portable electronic device such as, in particular, a timepiece, including a case made of a plastic material and delimited by a back cover and a lateral wall called the middle part, characterised in that this electronic device includes at least one means intended, via the effect of an application of pressure, to control at least one electronic function such as a horological function of said electronic device, this means, directed towards the interior of the case, being integral with said case and being set back with respect to the outer surface of the case, said means being able to be activated using a pointed element such as the tip of a pen.
As a result of these features, the present invention provides a means or control member which can be made of the same plastic material as the case, which means it can be manufactured, for example by injection moulding or moulding, at the same time as said case. This results in substantial savings in terms of manufacturing costs. Moreover, as this control member is set back with respect to the outer surface of the case, the aesthetic appearance of the electronic device according to the invention such as, for example, a watch, is greatly improved. The control member is in fact completely embedded in the case, so that said case is free of any projecting part or protuberance. Finally, the control member can no longer be activated inadvertently. Thus there is no longer a risk of, for example, a chronograph being inadvertently started, which means that the battery or accumulator is not run down unnecessarily. Likewise, adjustments such as, for example, that of the current time or an alarm time, cannot be modified without the user""s intervention.
According to another feature of the invention, the control means includes a stem connected to the case by a flexible portion which exerts a resilient return force on said stem.
The stem is of small dimensions, which allows it to be placed at any location on the case, for example on the middle part or in the back cover of said case. On the other hand, the flexible portion exerts a resilient return force on the stem via the effect of which said stem returns to its initial position, when the pressure exerted on it is released. It is thus no longer necessary to provide a return spring or a housing of a shape which is always complex in which said spring would housed. Due to its very simple construction, the control member according to the invention is thus inexpensive to manufacture.